# Objective
Forward perspective projections have poor floating point precision distribution over the depth range. Reverse projections fair much better, and instead of having to have a far plane, with the reverse projection, using an infinite far plane is not a problem. The infinite reverse perspective projection has become the industry standard. The renderer rework is a great time to migrate to it.
## Solution
All perspective projections, including point lights, have been moved to using `glam::Mat4::perspective_infinite_reverse_rh()` and so have no far plane. As various depth textures are shared between orthographic and perspective projections, a quirk of this PR is that the near and far planes of the orthographic projection are swapped when the Mat4 is computed. This has no impact on 2D/3D orthographic projection usage, and provides consistency in shaders, texture clear values, etc. throughout the codebase.
## Known issues
For some reason, when looking along -Z, all geometry is black. The camera can be translated up/down / strafed left/right and geometry will still be black. Moving forward/backward or rotating the camera away from looking exactly along -Z causes everything to work as expected.
I have tried to debug this issue but both in macOS and Windows I get crashes when doing pixel debugging. If anyone could reproduce this and debug it I would be very grateful. Otherwise I will have to try to debug it further without pixel debugging, though the projections and such all looked fine to me.
Makes some tweaks to the SubApp labeling introduced in #2695:
* Ergonomics improvements
* Removes unnecessary allocation when retrieving subapp label
* Removes the newly added "app macros" crate in favor of bevy_derive
* renamed RenderSubApp to RenderApp
@zicklag (for reference)
This is a rather simple but wide change, and it involves adding a new `bevy_app_macros` crate. Let me know if there is a better way to do any of this!
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# Objective
- Allow adding and accessing sub-apps by using a label instead of an index
## Solution
- Migrate the bevy label implementation and derive code to the `bevy_utils` and `bevy_macro_utils` crates and then add a new `SubAppLabel` trait to the `bevy_app` crate that is used when adding or getting a sub-app from an app.
